Hydrogen Fluoride-Catalyzed Addition of Carbon Monoxide to Propylene Under High Pressures*

Hydrogen Fluoride-Catalyzed Addition of Carbon Monoxide to Propylene under High Pressures* Yoshimasa Takezaki**, Yoshio Fuchigami**, Hiroshi Teranishi**, Nobuyuki Sugita** and Kiyoshi Kudo** Summary: Isobutyric acid forming reaction of propylene with carbon monoxide has been studied in the presence of HF-H2O catalyst under high pressures. The optimum conditions for the formation of acid have been decided as follows: water content of HF catalyst, 20 wt. %; charge ratio of HF to C3H6, 15 (mole ratio);reaction temperature,94℃ or lower;and the total pressure,190kg/cm2 or higher. Reaction temperature higher than 94℃ is unfavorable because of accelerated polymerization of C3H6. Reaction mechanism of the formation of isobutyric acid has been proposed, where the rate determining step, C3H7++CO(dissolved)→C3H7CO+, being first-order with regard to each reactant. The rate expression for the yield of the acid has been derived and the apparent activation energy of the over-all reaction has been found to be 21.7kcal/mole. Introduction Since 1933 when several patents1) on the production of carboxylic acids from olefins and carbon monoxide in acidic media were In these works Koch obtained good yield published, many works have been carried (better than 90%) of acids when butene or out2)-22)on this process. On propylene as an higher olefin was used8),9), but in the case of olefin, the first systematic study was reported propylene5), detailed data on experimental by Hardy in 19362), in which the author, conditions and yields were not reported except using 87 %-phosphoric acid as the catalyst, for the formations of alcohols, esters and observed 50% yield of total acids (isobutyric carboxylic acids as the products. Such pro- acid and higher acids)at 200℃ and 200 atm ducts as alcohols and esters are elucidated of carbon monoxide pressure. After 1955, to be formed as follows15): Koch and his co-workers have shown that R++HOH⇔ROH+H+, olefins react rapidly with carbon monoxide RCO++ROH⇔RCOOR+H+. at room temperature and under moderate Recently Friedman and Cotton14)～16)con- pressures in the presence of catalysts such firmed Koch's indication that anhydrous as concentrated sulfuric acid3)～8), phosphoric hydrogen fluoride is a powerful catalyst for acid9), anhydrous hydrogen fluoride5),8), mono- olefin-carbon monoxide reactions. However hydroxyfluoboric acid and its mixtures with they found that relatively minor amounts of phosphoric or sulfuric acid10) or aqueous water in the catalyst affect the reaction and BF311),12), and Koch has suggested the fol- the nature of the products obtained, so by lowing mechanism13),23): controlling water content in the catalyst they succeeded in obtaining fairly good yields of carboxylic acids, and for propylene they reported about 60%yield of acid at 75～100℃ * Received November 15 and 40 atm of carbon monoxide pressure . , 1965 ** Institute for Chemical Research In the present paper we wish to report , Kyoto University, Sakyo-ku, Kyoto. on the study carried out with the purposes Volume 8-June 1966 32 Takezaki, Fuchigami, Teranishi, Sugita and Kudo: Hydrogen Fluoride- to find the optimum conditions for isobutyric determined from the weight decrease of the acid formation in the hydrogen fluoride- weighing vessel and that of the latter from catalyzed reaction of propylene and carbon the pressure decrease of the reservoir. As monoxide under high pressures and to eluci- soon as the charging of carbon monoxide was date mechanism of the reaction from kinetic finished, the stirrer was started and that viewpoint. instant was defined as the zero-time of reaction. In the case of isobaric measurement, Experimental carbon monoxide gas was supplied almost Apparatus continuously so as to keep the total pressure The experimental apparatus consisted of constant at the desired point. an autoclave, a weighing vessel for propylene, After reaction, the solution in the auto- a reservoir of carbon monoxide (500ml in clave was poured on ice-water and extracted capacity) and Bourdon-type pressure gauges with n-hexane. The organic acids contained which was previously calibrated by a dead- in the hexane and water layers were analyzed weight pressure gauge. The autoclave, made respectively ; the quantity of total organic of stainless steel (50mm in inner diameter and acids in each layer was determined by alkali 328ml in capacity), had a magnetic stirrer titration and mole ratios among acids by gas and the rotating speed of the stirrer was chromatography. In the analysis of water watched by means of a stroboscope and layer, the solution was neutralized with NaOH controlled withinｱ50 r. p. m. The autoclave at first, then after drying the organic salts was heated by an electric furnace and the were extracted by methanol from NaF. The temperature of the vessel was maintained at methanol solution was dried again and the each experimental temperature withinｱ1.0℃ sodium salts of acids were dissolved in water, measured by a chromel alumel thermocouple and, after converting to free acids by ion- inserted in the hole bored in the wall of exchange resin the trace of HF remaining vessel. in the solution was removed off as CaF2. Materials Carbon monoxide was prepared by adding Results and Discussion formic acid to hot concentrated sulfuric acid, Preliminary experiments washed with aqueous caustic soda and com- In order to identify the products and to pressed into the reservoir up to about 300 find the optimum conditions for kinetic kg/cm2. The purity of the gas used was 97% measurements of the reaction, some pre- as determined by gas chromatography and liminary runs were carried out. the greater part of the impurity was air. 1) Identification of products : The organic Propylene was prepared by dehydration of acids produced were, as would be expected isopropyl alcohol through activated alumina from the results of previous investigators, at 375～400℃, and dried with CaCl2. The monocarboxylic acids of C4 as the major part crude propylene was purified by bulb-to-bulb and those of C7 as the remainder (hereafter distillation under vacuum. The purity was designated C4-acid and C7-acid, respectively). 99.97% as determined by gas chromatography. Carboxylic acids higher than C7 were not HF gas was obtained from Daikin Kogyo detected. Although in the products of the Co. Ltd. and the purity was determined to run under more severe conditions some be 99.5% by electric conductivity measure- amounts of dark brown oily matter were ment. obtained, which resulted from polymerization Procedure of propylene and might contain some kinds The weighed amount of HF-H2O mixture of higher acids. In the usual case of present at a desired mixing ratio was sucked into experiment such coloration were scarcely the pre-evacuated autoclave. After the auto- observed. clave attained an experimental temperature, As shown in Table 1, the C4-acid and C7- propylene and carbon monoxide were charged acids were identified to be isobutyric acid and into it, and the amount of the former was α-,γ-dimethylvaleric acid respectively from Bulletin of The Japan Petroleum Institute Catalyzed Addition of Carbon Monoxide to Propylene under High Pressures 33 Table 1. Identification of acids produced their boiling points, refractive indices, ele- mental analyses, molecular weights, gas chromatographies and infrared spectra. The C7-acid could not be identified by the infrared spectrum because of the lack of data on α-, γ-dimethylvaleric acid to be compared, but the absorption peaks observed could be re- garded as characteristic ones to monocarboxylic acids. Other isomers of C4- and Fig. 2-a Relation between water content of HF C7-acids were not detected by gas chroma- catalyst and yield of acids tography. 2) Reaction temperature: The relations between reaction temperature and the yield of total acids obtained when other conditions were fixed, are shown in Fig. 1. The curve shows the maximum yield at 94℃ and above this temperature the polymerization of propylene becomes pronounced as evidenced by the dark color of product solution. Fig. 2-b Relation between water content of HF catalyst and time spent for completion of reaction The curve shows the maximum yield at about 20wt. % water, but in the region of 13～ 20%the differences among the yields are only 10～15%. On the other hand, the water content shows much more remarkable effect on the reaction speed; as shown in Fig. 2-b, Fig. 1 Relation between temperature and yield of acids as to propylene charged the time spent for completion of reaction (defined by the time until the pressure de- 3) Water content of HF catalyst: The crease stops) is much prolonged with the effect of water content of HF catalyst on increase of water content. In these runs the the yield of total acids is shown in Fig. 2-a. mole ratio, HF/C3H6, was fixed at 5.0ｱ0.2. Volume 8-June 1966 34 Takezaki, Fuchigami, Teranishi, Sugita and Kudo: Hydrogen Fluoride- hence the water content 15wt.% corre- yields of acids, after the same duration in sponds to H2O/C3H6=1 and this ratio becomes both cases, coincided with each other within smaller with the decrease of water content. the accuracy of analysis. In another run, From stoichiometry of the acid forming reac- the speed was changed several times during tion, the condition such that the H2O/C3H6 the reaction but no discontinuity was observed ratio is smaller than 1 is unfavorable for on the curve of CO absorption. These results our purpose and C3H6 in excess of the stoi- suggest that the diffusion process can not be chiometry may be consumed by polymerization the rate-determining step if the speed is reaction. As shown in Figs. 2-a and 2-b, more than 600 r.p.m. under the present ex- the decreasing tendency of the acids yield perimental conditions.

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